Delay Differentiation without Rate Tinkering

Link buffering is a key element in packet-switched networks to absorb temporary traffic bursts without excessive dropping. The resulting queuing delay is a critical performance factor. Research on buffer management typically studies differentiated buffer allocation to control forwarding rates or buffer size management to control the overall queuing delay. On the other hand, delay differentiation is typically accomplished by packet scheduling and thus implies rate differentiation. In this paper a radically simpler approach to delay differentiation through buffer management is studied. Instead of actively managing throughput, Delay Differentiated FIFO (DDF) uses a simple drop-based mechanism to offer multiple delay classes, but closely tracks the per-class throughput of the corresponding single-class FIFO queuing system. End systems choose which delay class best balances their loss and delay requirements. Architecturally, DDF does not interfere with management and policy decisions at end and edge systems and does not add another control loop to the existing mix of traffic management techniques. The forwarding characteristics of DDF are analyzed using stochastic models. Refinements to the basic algorithm are presented and it is shown how DDF can be implemented with very little execution overhead compared to FIFO. Packet-level simulation results are presented to complement the analytical findings.